The invention relates to a method for making polvaspartic esters.
Two-component coating compositions having a polyisocyanate component and an isocyanate-reactive component (a polyhydroxyl component) are known. These compositions are suitable for the preparation of high quality coatings that may be rendered rigid, elastic, resistant to abrasion and to solvents and, above, all, resistant to weathering. Polyaspartic esters have been used as isocyanate-reactive components in such two-component compositions. A polyaspartic ester can be used individually, with a polyisocyanate, or possibly in combination with polyols or polyamines. Alternatively, polyaspartic esters can be used with blocked polyamines such as ketimines, aldimines or oxizolidines.
Methods for making polyaspartic esters are known. It is known, for instance, that during the Michael Addition Reaction of an ester of fumaric or maleic acid and the primary amine, for instance, the ester of maleic or fumaric acid isomerizes to dialkyl fumarate in the presence of amines, according to the following chemical reaction: 
The dialkyl fumarate is then converted to a polyaspartic ester. Mixtures of polyaspartic esters based on cyclic and acyclic amines have proven to be valuable isocyanate-reactive components of polyurea compositions that have found utility in the formulation of high solids coatings where solvent content is very low or zero. These formulations are used in architectural and automotive refinish applications. Known methods for preparing polyaspartic ester mixtures typically involve preparing polyaspartic esters based on acyclic and cyclic amines separately and then combining each polyaspartic ester mixture. Polyaspartic esters based on acyclic amines, which contain amines attached to primary carbons, generally react with an isocyanate faster than polyaspartic esters based on cyclic amines that have an amine group attached to a secondary ring carbon. In addition, polyaspartic esters based on acyclic amines have a lower viscosity than polyaspartic esters based on cyclic amines. It is often desirable to blend these types of amines to achieve formulations with different viscosities and with intermediate reaction speeds.
U.S. Pat. No. 5,236,741 and U.S. Pat. No. 5,623,045 each disclose a single step process for the production of polyaspartic esters. Each process reacts an ester of maleic or fumaric acid with a primary polyamine such that preferably one olefinic double bond is present for each primary amino group. The patents teach that excess starting materials is removed by distillation after the reaction. Neither patent discusses how much time it takes for the reaction of the ester of maleic or fumaric acid to complete, i.e., to obtain a yield of about 100% of the polyaspartic ester. Neither patent addresses the issue of developing a process that makes a 100% yield of a mixture of (1) a polyaspartic ester based on a cyclic amine and (2) a polyaspartic ester based on an acyclic amine in a matter of days.
Unfortunately, such methods have prevented manufacturers of polyaspartic esters from delivering shipments to customers as quickly as would be desired. I have discovered that by following the teachings of the above-described known methods and using a 1:1 stoichiometric ratio, it takes several months to obtain full, or near-full, conversion of the reaction of a cyclic amine and an ester of maleic or fumaric acid. For instance, the use of bis (4-aminocyclohexyl)methane requires the polyaspartic ester to be stored in excess of six weeks to achieve 95% reaction and from six to twelve months to achieve complete reaction; and the use of bis (3-methyl-4-aminocyclohexyl)methane [commercially known as Laromin C-260] requires the polyaspartic ester to be stored in excess of eight weeks to achieve 95% reaction and from twelve to eighteen months to achieve 100% reaction. Removing excess ester of maleic or fumaric acid, as suggested by U.S. Pat. Nos. 5,236,741 and 5,623,045, is a time-consuming expensive procedure.
The problem of long waiting times has not been able to be resolved by making large amounts of the mixtures in advance because it is extremely difficult to predict customers"" needs for the mixtures. Further, expensive storage, and inventory costs have discouraged the making and the storing of large amounts of the mixtures. As such, it is not uncommon for a customer to have to wait several months to receive an order of mixtures of polyaspartic esters.
It would be advantageous to develop an improved method for making mixtures of polyaspartic esters based on cyclic amines and polyaspartic esters based on acyclic amines that overcomes the above-named disadvantages.
The invention relates to a method for making a polyaspartic ester mixture in-situ comprising the sequential steps of (a) reacting a cyclic amine with an excess amount of an ester of fumaric or maleic acid to form a mixture containing first polyaspartic ester component and excess unreacted ester of fumaric or maleic acid, and (b) adding an acyclic amine to the mixture resulting from step (a) and reacting the acyclic amine with the excess ester of fumaric or maleic acid to form a second polyaspartic ester component. The invention is also directed to the in-situ mixture of polyaspartic ester esters formed during the method, prior to termination of the process, that contains the first polyaspartic ester component and the second polyaspartic ester component. The method makes it possible for customers to receive mixtures of the polyaspartic esters in a fraction of the time it has ordinarily taken. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
As used in this application, the term xe2x80x9ccyclic aminexe2x80x9d refers to an amine that has at least one primary amine group attached to a cyclic group, e.g., an amine attached to a secondary ring carbon. The term xe2x80x9cacyclic aminexe2x80x9d refers to an amine that does not have a primary amine group attached to a cyclic.
The invention is based on the discovery that mixtures of polyaspartic esters based on cyclic amines and polyaspartic esters based on acyclic amines can be prepared in-situ, (under certain conditions) in a fraction of the time it ordinarily takes to make them. It is critical that the cyclic amine first react with an excess ester of maleic or fumaric acid. As discussed below, if the sequence of the steps varies, e.g., if the steps are reversed or if the cyclic and acyclic amines are added simultaneously, the reaction proceeds substantially slower and is outside the scope of the present invention.
The first and second ester components are selected from esters of maleic acid and fumaric acid. Esters of maleic acid and fumaric acid include suitable dialkyl maleates or dialkyl fumarates. Suitable dialkyl maleates include, diethyl maleate, dipropyl maleate, dibutyl maleate, methyl propyl maleate, ethyl propyl maleate, and the like. Suitable dialkyl fumigates include, diethyl fumurate, dipropyl fumurate, dibutyl fumurate, methyl propyl fumurate, ethyl propyl fumurate, and the like. Generally, dimethyl maleate or dimethyl fumurate is not used in an appreciable amount because it has been discovered that these esters cause the precipitation of long needle-like crystals that no longer participate in the Michael Addition Reaction and that cause the reaction to stop altogether. It is believed that cinnamate esters do not react under the same reaction conditions as esters of maleic acid or fumaric acid.
The amine component is generally selected from difunctional or trifunctional cyclic and acyclic amines that can accomplish the objects of the invention. Suitable amines can be selected from the following. Suitable acyclic difunctional amines include but are not limited to ethylene diamine, 1,2-diaminopropane, 1,4-diaminobutane, 1,6-diaminohexane, 2,5-dimethylhexane, 2,2,4- and/or 2,4,4-trimethyl-1,6-diaminohexane, 1,11-diaminoundecane, 1,12-diaminododecane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane, 2,4- and/or 2,6-hexahydrotolylenediamine, 2,4xe2x80x2-and/or 4,4xe2x80x2-diaminodicyclohexylmethane, and 3,3xe2x80x2-dimethyl-4,4xe2x80x2-diaminodicyclohexylmethane. Suitable cyclic amines include aromatic polyamines such as 2,4- and/or 2,6-diaminotoluene, and 2,4xe2x80x2- and/or 4,4xe2x80x2-diaminodiphenyl-methane are also suitable but less preferred. Other suitable cyclic amines include Bis- (3-methyl-4aminocyclohexyl) methane, 2,4-diamino-1-methyl, cyclohexane, and 2,6-diamino-1-methyl cyclohexane. Suitable trifunctional amines include 4-aminomethyl-1,8-diaminooctane (also known as triaminononane supplied by Monsanto Company), tris-(2-aminoethyl)amine. It is believed that tetrafunctional amines, e.g., N,N,Nxe2x80x2,Nxe2x80x2-tetrakis-(2-aminoethyl)-1,2-ethanediamine are also suitable.
The polyisocyanate component used to react with the polyaspartic ester mixtures includes any polyisocyanate, which when used in accordance with the invention, meets the object of the invention. Suitable polyisocyanate for use as polyisocyanate component in accordance with the present invention include the known polyisocyanate of polyurethane chemistry. Examples of suitable low molecular weight polyisocyanate having a molecular weight of 168 to 300 include 1,4diisocyanatobutane, 1,6-hexamethylene diisocyanate, 2,2,4- and/or 2,4,4-trimethyl-1,6-hexamethylene diisocyanate, dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 2,4xe2x80x2- and/or 4,4xe2x80x2-diisocyanato-dicyclohexyl methane, 2,4- and/or 4,4xe2x80x2-diisocyanatodiphenyl methane and mixtures of these isomers with their higher homologues that are obtained in a known manner by the phosgenation of aniline/formaldehyde condenses, 2,4- and/or 2,6-diisocyanatotoluene and any mixtures of these compounds. Preferred cyclic isocyanates include diphenylmethane 4,4xe2x80x2-diisocyanate (MDI), diphenylmethane 2,4xe2x80x2-diisocyanate, 2,4- and/or 2,6-diisocyanatotoluene. Preferred aliphatic isocyanates include hexamethylene diisocyanate, isophorone diisocyanate, 2,4xe2x80x2- and/or 4,4xe2x80x2-diisocyanato-dicyclohexyl methane.
Additional suitable polyisocyanate components include derivatives of the above-mentioned monomeric polyisocyanate, as is conventional in coatings technology. These derivatives include polyisocyanate containing biuret groups as described, for example, in U.S. Pat. Nos. 3,124,605 and 3,201,372 and DE-OS 1,101,394, incorporated herein by reference in their entirety; polyisocyanate containing isocyanurate groups as described in U.S. Pat. No. 3,001,973, DE-PS 1,022,789, 1,222,067 and 1,027,394 and DE-OS 1,929,034 and 2,004,048, incorporated herein by reference in their entirety; polyisocyanate containing urethane groups as described, for instance, in DE-OS 953,012, BE-PS 752,261 and U.S. Pat. Nos. 3,394,164 and 3,644,457; polyisocyanate containing carbodiimide groups as described in DE-PS 1,092,007, U.S. Pat. No. 3,152,162 and DE-OS 2,504,400, 2,537,685 and 2,552,350, incorporated herein by reference in their entirety; and polyisocyanate containing allophanate groups as described, for example, in GB-PS 994,890, BE-PS 761,626 and NL-OS 7,102,524. Suitable polyisocyanate also include polyisocyanate that contain uretdione groups. In one embodiment, asymmetric trimers such as those in U.S. Pat. No. 5,717,091, incorporated herein by reference in its entirety. Isocyanate group-containing prepolyrners and semi-prepolymers based on polyisocyanate can also be used as the polyisocyanate component. These prepolymers and semi-prepolymers generally have an isocyanate content ranging from about 0.5 to 30% by weight, preferably about 1 to 20% by weight, and are prepared in a known manner by the reaction of starting materials, e.g., isocyanate-reactive compounds such as polyols, at an NCO/OH equivalent ratio of about 1.05:1 to 10:1, preferably about 1.1:1 to 3:1.
The first step of the process involves reacting a cyclic amine with an excess amount of an ester of fumaric or maleic acid to form a mixture containing first polyaspartic ester component and excess unreacted ester of fumaric or maleic acid. The equivalent ratio of the ester of maleic or fumaric acid to the cyclic polyamine is greater than 1:1, preferably 1.2:1 to 5:1 and more preferably 1.4:1 to 3:1. Generally, the more excess ester of maleic or fumaric acid used, the faster the initial reaction proceeds. To obtain a yield that is about 100% at a ratio of ester of maleic or fumaric acid to cyclic amine of 2:1, for instance, the reaction lasts less than 24 hours. When the number ratio of ester of maleic or fumaric acid to cyclic amine of 5:1, for instance, the reaction lasts less than 8 hours. It is generally preferred to have the initial reaction to be complete in about eight hours. Actual ratios for a specific application can be determined by routine experimentation.
The second step of the process involves adding an acyclic amine to the mixture and reacting the acyclic amine with the excess ester of fumaric or maleic acid to form a second polyaspartic ester component. The acyclic amine is preferably used in an amount that corresponds to the excess, unreacted ester of fumaric or maleic acid. Accordingly, the equivalent ratio of acyclic amine to cyclic amine is preferably 0.2:1 to 4:1, preferably 0.4:1 to 2:1. The reaction of the excess ester of maleic or fumaric acid and the acyclic amine generally takes less than two weeks.
The reaction conditions at which the method is carried out under are discussed below. Generally, the reaction takes place at a temperature of 0 to 100xc2x0 C. The reaction may take place in the absence or in the presence of suitable solvents such as methanol, ethanol, propanol, ethyl- or butyl acetate and mixtures of these solvents. The pressure of the reaction is generally atmospheric. As such, since the reaction of the cyclic polyamine and the ester of maleic or fumaric acid lasts hours instead of months, conversions of about 100% of mixtures of the polyaspartic ester based on the cyclic amine and the polyaspartic ester based on the acyclic amine can be obtained in days instead of months. Generally, a conversion of about 100% is obtained in less than 10 to 14 days.
The polyaspartic ester mixtures can be used in applications such as coatings. The low viscosity allows the formulation of paint at high or very high solids, or even paint with no solvent. Coatings applications can use polyurea coatings based on polyaspartic esters and polyisocyanate include general factory applied coating and field applied architectural or automotive refinish coatings.
The invention will now be described in the following illustrative examples. All percentages given are by weight unless otherwise indicated.